1. Technical Field
The present invention relates to apparatus for coating articles, and particularly to coating apparatus for forming coatings of epoxy or other synthetic resin or paint on steel or other metal articles requiring protection against corrosion or requiring insulation, or other treatment.
2. Description of the Prior Art
The prior art contains many coating apparatus wherein articles are dipped in a series of tanks containing cleaning, precoating coating, and post-coating treatment solutions to produce a film or deposit of liquid or particulate coating material thereon. The articles are then passed through an oven where the coating is dried and cured to form a durable corrosion resistant or insulative layer on the article.
In one typical prior art apparatus, a plurality of tanks containing various treating fluids are disposed along a linear path above which is mounted an elongated oven. A conveyor track section which is movable between raised and lowered positions extends over the tanks for immersing batches of articles carried by carriers on the conveyor track. The articles are loaded upon the carriers at a front station of the coating apparatus, and the loaded carriers are pushed along the track section in increments by a pawl mechanism when the track section is raised so as to advance the carriers sequentially to each tank. A typical arrangement of tanks includes one or more initial tanks for cleaning the metal articles, for example a first tank containing water or detergent along with ultrasonic facilities for removing heavy soil, particles, and the like, a second tank containing a stronger cleaner such as an acid bath for removing contaminant films and other impurities, and a third tank containing a water rinse. This is followed by several tanks containing respective precoating treatment solutions such as a surface conditioner, a zinc phosphate treatment, a water rinse, a sealer and deionized water rinsing baths prior to the coating bath which can be an electrocoating bath containing a suspension of epoxy and other resin particles. Several permeate wash baths and/or sprays are in the last several tanks.
The apparatus includes an elevator at the rear end of the apparatus for raising each carrier, as it is advanced from the last tank, upward into the oven wherein the carriers are incrementally advanced along a stationary conveyor track from the rear to the front by a pawl mechanism operated in synchronism with the advancement of the carriers on the lower track. A burner mounted at the rear of the oven heats the air in the over while an externally mounted return duct and circulating fan provide for air circulation from the back to the front of the oven. The oven has a front opening which is closed between carrier advancing periods by a collapsible door formed by a plurality of rigid horizontal strips which, when raised, close the front opening, and which, when lowered, collapse to permit the next carrier to exit the front opening of the oven. At the front of the apparatus, an elevator is provided for receiving each carrier as it exits the oven and for lowering each carrier to the work area where the articles with completed coatings are removed from the carriers and new articles to be treated are placed thereon. Additionally, the typical prior art facility contains air exhaust systems for withdrawing excess air from the oven in order to maintain proper drying and curing conditions, and for withdrawing heated air from the work area to provide comfortable working conditions for workers in the loading area.
The prior art coating apparatus utilized in relatively large scale commercial production facilities are generally designed and assembled at the location where they are employed. Tools, equipment and trained personnel are often required to travel long distances in order to manufacture and/or assemble various components of the coating apparatus at the plant location. For these reasons, costs of installing a coating apparatus for employment in a commercial scale operation are relatively high. This relatively high cost inhibits employment of coating processes on many articles and/or further increases costs due to shipment of articles to other locations where the volume of articles being coated warrants the expense of the coating apparatus. Additionally, if a plant location is closed, the disassembly, shipment of disassembled parts and reassembly at a new plant location is expensive.